This invention relates to a printing apparatus and printing control method. More particularly, the invention relates to a printing apparatus and printing control method for discharging ink droplets in accordance with the ink-jet method and printing character, images and the like on a recording medium.
An ink-jet printing apparatus known in the art performs printing by discharging extremely small ink droplets from a printhead. In comparison with other types of printing apparatus, such an ink-jet printing apparatus not only produces little noise, makes possible high-speed printing and facilitates color printing but also can be used to print on printing media such as plain paper as a matter of course and fabric as well. The apparatus makes high-quality printing possible.
In general, the printhead of an ink-jet printing apparatus has one to two thousand orifices which discharge ink droplets. The printhead is caused to scan in relative to the printing medium to thereby perform printing over the entire area of the printing medium. In an actual printing operation, the printhead is mounted on a carriage, the carriage is moved back and forth along the traveling path thereof (the traveling direction is referred to as the xe2x80x9cmain-scan directionxe2x80x9d), and the printing medium is conveyed in a direction (referred to as the xe2x80x9csub-scan directionxe2x80x9d) orthogonal to the carriage traveling direction a prescribed amount whenever the carriage is moved back and forth one time.
Usually an arrangement is adopted in which the printhead mounted on the carriage is mounted on the carriage removably or in which an ink tank containing the ink supplied to the printhead is removably attached to the printhead.
Thus, the structure of the conventional ink-jet printing apparatus is such that the ink tank is removably attached to the carriage or to the printhead. This makes it necessary for the printing apparatus to check automatically whether the ink tank has been installed in the printing apparatus correctly at the time of printing.
FIG. 11 is a perspective view showing a conventional detection principle for detecting whether an ink tank has been installed.
As shown in FIG. 11, an ink tank 102 containing ink 101 has a bottom provided with a light reflecting surface 103. A light-emitting element 104 such as an infrared LED emits light that is reflected by the light reflecting surface 103. The reflected light is received by a light-receiving element 105 such as a phototransistor. In a case where the ink tank 102 has been mounted correctly on the carriage of a printing apparatus, the light emitted by the light-emitting element 104 is reflected by the light reflecting surface 103 and reaches upon the light-receiving element 105. The latter converts the light to an electric signal in accordance with the amount of light received and issues an output signal (I) serving as a detection signal indicating that the ink tank has been installed.
If the ink tank 102 has not been mounted on the carriage, on the other hand, the light emitted by the light-emitting element 104 continues traveling straightforward and is not returned to the light-receiving element 105 owing to the absence of a reflecting body. Thus an electric signal generated by the light-receiving element 105 varies, depending in whether the ink tank 102 is mounted or not.
Thus, whether or not the ink tank is present can be discriminated based upon the erectric signal generated by the light-receiving element 105.
More specifically, let I represent the electric signal output by the light-receiving element 105. If the ink tank has been installed correctly, the electric signal output I will be I1. If the ink tank has not been installed, however, the electric signal output I of the light-receiving element 105 will be xe2x80x9c0xe2x80x9d. This conventional art assumes that no extraneous light enters into the apparatus. Thus, the output of the light-receiving element 105 differs depending upon whether the ink tank is present or not.
If xcex1 is decided beforehand to satisfy the inequality 0 less than xcex1 less than I1 and the output (I) of the light-receiving element 105 is greater than xcex1, then it is judged that the ink tank 102 has been installed.
In the prior art, the ink-jet printing apparatus is provided with means inclusive of a sensor, which is fixed to the main body of the apparatus, for automatically detecting existence/absence of ink in the ink tank by utilizing the movement of the carriage and alerting the user based upon the result of the sensing operation. For example, the residual ink detection means includes electrodes provided within the ink tank and measures the electrical conductivity between the electrodes or is adapted to sense discharged ink droplets optically. In general, the method using the electrodes results in a more complicated structure for the ink tank itself. For this reason, the most usual practice is to adopt the means for detecting existence/absence of ink in optical fashion.
An ink-jet printhead or an ink tank equipped with detecting means for optically detecting residual ink is disclosed in the specifications of Japanese Patent Application Laid-Open (KOKAI) Nos. 60-31021, 2-102062 and 7-218321.
FIG. 12 is a diagram showing an example of the conventional arrangement of an ink detection unit for optically detecting whether ink is present or not.
As shown in FIG. 12, the ink tank 102, which comprises a member such as semi-transparent plastic having a light transmitting property, accommodates ink 101. The bottom of the ink tank 102 is formed to have an optical prism 106 that performs the function of an optical ink sensing unit. Here the optical prism 106 is a triangular prism having an apex angle of 90xc2x0. The optical prism 106 consists of a nearly transparent material such as polypropylene and is formed as an integral part of the ink tank 102.
Light emitted from the light-emitting element 104 under conditions in which there is no ink in the ink tank 102 reaches the light-receiving element 105 upon being reflected at boundary surfaces 106A, 106B between the optical prism 106 and ink 101. Let the electric signal output,I from the light-receiving element 105 under these conditions be represented by I2.
Under conditions where the ink tank 102 is filled with the ink 101, the reflectance of the emitted light at the boundary surfaces 106A, 106B differs from that in the absence of ink owing to the refractive indices of the ink tank 102 itself and ink 101. As a result, there is a reduction in the amount of light from the light-emitting element 104 that arrives at the light-receiving element 105 via the boundary surfaces 106A, 106B. Accordingly, the output (I) of the light-receiving element 105 in this case satisfies the equation I=I3 less than I2. Thus, it is possible to detect whether or not the ink 101 is present within the ink tank 102 based upon the amount of light sensed by the light-receiving element 105.
Thus, the output of the light-receiving element 105 differs depending upon whether the ink 101 is present or not.
If xcex2 is decided beforehand to satisfy the inequality 0 less than I3 less than xcex2 less than I2 and the output (I) of the light-receiving element 105 is greater than xcex2, then it is judged that there is no ink in the ink tank 102.
However, various factors in addition to the light from the light-emitting element 104 contribute to the output of the light-receiving element 105 and cause the output to fluctuate.
For example, the phototransistor used in the light-receiving element 105 produces current (referred to as xe2x80x9cdark currentxe2x80x9d) even when it is not receiving light. The output of dark current depends upon the ambient temperature and rises exponentially as the temperature rises. In addition, there is the possibility that extraneous light, not the light for which the light-emitting element 104 is the source, will reach upon the light-receiving element 105. The extraneous light is such that the amount of incident light varies depending upon angle of incidence with respect to the light-receiving element 105 and, as a result, the output of the light-receiving element 105 varies.
Thus, the output of the light-receiving element 105 is influenced greatly by dark current and by the surrounding environment, such as extraneous light. Consequently, it is very difficult to decide xcex1 and xcex2 in advance so as to satisfy the above-mentioned conditions independently of the environment.
In order to eliminate the influence of dark current, it is possible to provide a thermal insulating mechanism or temperature correction circuit in order to hold the temperature of the light-receiving element 105 constant. This is disadvantageous, however, in that it raises the cost of the apparatus. To eliminate the effects of extraneous light, the interior of the apparatus can be structured so that extraneous light will not enter. To print on a printing medium, however, it is required that the printing apparatus must have openings, namely a paper feed port through which printing paper (the printing medium) is fed into the apparatus from the outside, and a paper discharge port from which the printing paper is discharged to the exterior of the apparatus after the paper is printed on. The presence of these openings makes it very difficult to realize a structure that does not allow light to enter the interior of the apparatus.
Accordingly, an object of the present invention is to provide an low-cost printing apparatus in which it is possible to judge accurately, regardless of the surrounding environment, whether an ink tank or ink is present or not, as well as a method of controlling printing in such an apparatus.
According to one aspect of the present invention, the foregoing object is attained by providing a printing apparatus for supplying ink from an ink tank, which includes a light reflecting portion used for optically detecting whether or not ink is present, or whether or not the ink tank is present, and performing printing using a printhead according to an ink-jet method, the apparatus comprising:
a light-emitting unit for emitting light to the light reflecting portion; a light-receiving unit for receiving light; difference calculating means for calculating a difference between a first signal, which is obtained from light received by the light-receiving unit in a case where the light-emitting unit emits the light, and a second signal, which is obtained from light received by the light-receiving means in a case where the light-emitting means emits no light;
judgment means for judging whether or not ink is present and/or whether or not the ink tank is present, based upon the difference calculated by the difference calculating means with a predetermined threshold value.
Preferably, the judgement means includes comparison means for comparing the difference obtained by the difference calculating means with a predetermined threshold value, and the judgment means judges whether or not ink is present, or whether or not the ink tank is present, based on result of comparison by the comparison means.
Preferably, the ink tank has a plurality of light reflecting portions, the plurality of light reflecting portions includes a first light reflecting portion used for optically detecting whether or not ink is present and a second light reflecting portion used for optically detecting whether or not the ink tank is present, and the judgment means judges whether or not ink in the ink tank is present based on result of detection by the first light reflecting potion, while judges whether or not the ink tank is present based on result of detection by the second light reflecting portion.
Preferably, the apparatus further comprises printing control means for performing printing control in accordance with the judgment made by the judgment means. Note that the printing control way include suspension of printing, display of a message prompting replacement or attachment of the ink tank and resumption of printing.
Preferably, the first light reflecting portion is a light-transmissive optical prism provided on a bottom surface of the ink tank, and the second light reflecting portion is a light reflecting surface provided on the bottom surface of the ink tank.
The apparatus may further comprise a scanning unit mounting an ink cartridge integrating the printhead and the ink tank, and reciprocally moving the ink cartridge. It is further preferable that the first and second light reflecting portions are provided along scanning directions of the scanning unit.
In a preferred embodiment, the light-emitting unit and the light-receiving unit are provided in the vicinity of a traveling path of the ink cartridge, the light-emitting unit is an LED for emitting infrared light, and the light-receiving unit is a phototransistor for receiving the infrared light and converting the received infrared light to an electric signal.
In a preferred embodiment, an arrangement may be adopted in which the first and second signals are obtained at the same position where the ink tank is situated on the traveling path of the ink cartridge. In this case the signals can be obtained when the ink cartridge is stopped immediately above a position at which the light-emitting unit and light-receiving unit are provided.
Alternatively, in another preferred embodiment, the light-emitting unit is controlled in such a manner that a plurality of the first signals are obtained while the ink cartridge is beng moved in the vicinity of the position at which the light-emitting unit and light-receiving unit are provided, a maximum value of the first signals is calculated from the plurality of the first signals obtained by this control, and control is performed so as to stop emission of light by the light-emitting means and obtain the second signal by the light-receiving unit at a location at which the maximum value of the first signals is obtained.
In still another preferred embodiment, control is performed in such a manner that a plurality of each of the first and second signals are obtained while the ink cartridge is being moved in the vicinity of the position at which the light-emitting unit and light-receiving unit are provided, a difference is obtained between the first and second signals, from the pluralities of first and second signals obtained by this control, at each position where positions at which the pluralities of first and second signals are acquired correspond, a maximum value of a plurality of these differences is calculated, the maximum value of the differences obtained is compared with a predetermined threshold value and whether or not the ink tank is present is judged, based upon the result of the comparison.
The printhead preferably is provided with an electrothermal transducer for generating thermal energy applied to the ink in order to discharge the ink by utilizing thermal energy.
According to another aspect of the present invention, the foregoing object is attained by providing a printing control method used when supplying ink from an ink tank, which includes a first light reflecting portion used for optically detecting whether or not ink is present, or whether or not the ink tank is present, and performing printing using a printhead according to an ink-jet method, the method comprising:
a first signal acquisition step of acquiring a first signal obtained from light received at a light-receiving portion in a case where the light reflecting portion is irradiated with light; a second signal acquisition step of acquiring a second signal obtained from light received at the light-receiving portion in a case where the first and/or second light reflecting portions are not irradiated with light; a difference calculation step of calculating a difference between the first and second signals; a judgment step of judging whether or not ink is present and/or whether or not the ink tank is present, based upon the difference obtained at the difference calculation step with a predetermined threshold value; and a printing control step of performing printing control in accordance with the judgment resultrendered at the judgment step.
In accordance with the present invention as described above, when printing by a printhead according to an ink-jet method by supplying ink from an ink tank, which has a light reflecting portion used to optically detect whether or not ink is present, or whether or not an ink tank is present, a difference is obtained between a first signal, which is obtained from light received at a light-receiving portion in a case where the light reflecting portion is irradiated with light, and a second signal, which is obtained from light received at the light-receiving portion in a case where the first and second light reflecting portions are not irradiated with light, and whether or not ink is present, or whether or not the ink tank is presented is judged based upon the difference is compared with a predetermined threshold value.
The invention is particularly advantageous in that even if noise that affects the judgment concerning existence/absence of the ink or ink tank is produced at the light-receiving portion or even if extraneous light accidentally reaches upon the light-receiving portion, such influence can be eliminated so that judgment concerning the presence/absence of the ink and/or ink tank can be rendered accurately.
Further, since special components are not necessary to achieve the above-mentioned effects, another advantage is that the judgment concerning the presence/absence of the ink and/or ink tank can be rendered accurately at low cost.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.